The present invention relates to an anisotropic conductive film to be interposed between a semiconductor element and a circuit board to form an electrical connection between them, and to a production method thereof.
An anisotropic conductive film (hereinafter to be also referred to as ACF) can establish electrical connection merely by insertion thereof between a semiconductor element and a circuit board and application of a pressure. The simple and easy handling that is available with ACF has produced a growing demand in recent years on its use in high precision semiconductor elements. A typical ACF is obtained by dispersing conductive particles in a film made from an adhesive insulating material.
However, the conventional ACF is associated with a difficulty in achieving fine pitch connection and a need to use a convex terminal (e.g., bump contact) as a connection terminal of a semiconductor element.
To solve these problems, Japanese Patent Application No. 9-117244 (WO 98/07216) proposes an ACF prepared by penetrating plural conductive paths in the thickness direction of an insulating film.
In the proposed ACF, an electrical connection has been established between a semiconductor element and a circuit board with the aid of a conductive path capable of making contact with both an electrode of the semiconductor element and a circuit of the circuit board.
The conductive paths incapable of making contact with an electrode of a semiconductor element and a circuit of a circuit board do not contribute to the electrical connection. The both ends of these conductive paths make contact with the semiconductor element at some place else but the electrode and with the circuit board at some place else but the circuit, only when a pressure is applied.
When, however, an end on the semiconductor element side touches a part other than an electrode of the semiconductor element, a passivation layer formed on the semiconductor element may be broken depending on the shape of the semiconductor element, and a fine circuit wiring on the semiconductor element may be deformed, causing damage on the semiconductor element. Damaged semiconductor elements tend to suffer from a short failure or open failure.
When the end on the side of the circuit board is under contact with a circuit board at a part other than a circuit, the circuit may have lower connection reliability. Such lower connection reliability is highly likely to occur particularly when a resist formed on the circuit board is thicker than the circuit itself.
It is therefore an object of the present invention to solve the above-mentioned problems and provide an anisotropic conductive film free of contact between a conductive path irrelevant to the electrical connection, and a semiconductor element at a part other than an electrode and/or a circuit board at a part other than a circuit, as well as a production method thereof.
The ACF of the present invention is interposed between a semiconductor element and a circuit board to make an electrical connection and is characterized by the following embodiments.
(Embodiment 1) Plural conductive paths insulated from each other penetrate an insulating film in the thickness direction of the film, with the both ends of the paths being exposed on the surface of the insulating film, wherein a conductive path capable of touching an electrode of a semiconductor element has an end on the semiconductor element side protruding more than an end on the semiconductor element side of a conductive path incapable of contact with the electrode.
(Embodiment 2) Plural conductive paths insulated from each other penetrate an insulating film in the thickness direction of the film, with the both ends of the paths being exposed on the surface of the insulating film, wherein a conductive path capable of touching a circuit of a circuit board has an end on the circuit board side protruding more than an end on the circuit board side of a conductive path incapable of contact with the circuit.
(Embodiment 3) Plural conductive paths insulated from each other penetrate an insulating film in the thickness direction of the film, with the both ends of the paths being exposed on the surface of the insulating film, wherein a conductive path capable of touching an electrode of a semiconductor element and a circuit of a circuit board has both ends protruding more than both ends of a conductive path incapable of contact with the electrode and the circuit.
According to the present invention, a conductive path in ACF, which is capable of contact with the electrode of a semiconductor element and/or the circuit of a circuit board, can protrude from the insulating film.
A conductive path in ACF of the present invention, which is incapable of contact with the electrode of a semiconductor element and/or the circuit of a circuit board, may be recessed from the surface of the insulating film. This conductive path may have an insulating layer formed on an end thereof.
The Embodiment 1 of the ACF of the present invention can be produced by the following steps.
(a) Forming plural conductive rods in an insulating film in such a manner that the rods are insulated from each other and penetrate the film in the thickness direction thereof.
(b) Extending, of the plural rods, a rod capable of contact with an electrode of a semiconductor element and/or shortening a rod incapable of such contact, so that the rod capable of contact with the electrode has an end on the semiconductor element side protruding more than an end on the semiconductor element side of the rod incapable of contact.
The Embodiment 2 of the ACF of the present invention can be produced by the following steps.
(a) Forming plural conductive rods in an insulating film in such a manner that the rods are insulated from each other and penetrate the film in the thickness direction thereof.
(b) Extending, of the plural rods, a rod capable of contact with a circuit of a circuit board and/or shortening a rod incapable of such contact, so that the rod capable of contact has an end on the circuit board side protruding more than an end on the circuit board side of the rod incapable of contact.
The Embodiment 3 of the ACF of the present invention can be produced by the following steps.
(a) Forming plural conductive rods in an insulating film in such a manner that the rods are insulated from each other and penetrate the film in the thickness direction thereof.
(b) Extending, of the plural rods, a rod capable of contact with an electrode of a semiconductor element and a circuit of a circuit board and/or shortening a rod incapable of such contact, so that the rod capable of contact has both ends protruding more than both ends of the rod incapable of contact.
According to the production method of the present invention, one or both ends of a rod capable of contact may be extended by deposit of a conductive material thereon.
According to the production method of the present invention, moreover, one or both ends of a rod incapable of contact may be shortened by etching.